1. Field of the invention
The present invention relates to a throttle valve control system for controlling the opening of the throttle valve of an internal combustion engine.
2. Description of Background Information
Various measures have been proposed for improving fuel economy of an internal combustion engine. The lean burn system characterized by the supply of a lean air-fuel mixture, the generation of swirling action in the combustion chamber for enhancing sufficient mixture flow in the combustion chamber, or the improvement of the shape of the combustion chamber, are examples of such measures. However, in those systems, there has been a problem that the structure of the system generally becomes complicated, so that an increase of the cost is not avoided. One method for solving the above problem is to provide a system for controlling the opening of the throttle valve of the engine. For example, Japanese Patent Application Laid Open No. P60-192843 discloses a control of the throttle valve opening in which the throttle valve opening is determined simply in accordance with the operation position of the accelerator pedal and the engine rotational speed. Therefore, the improvement of the fuel economy was not gained by such a throttle valve opening control.
If the throttle valve opening is controlled for the purpose of fuel economy only, the throttle valve may not be fully opened even if the accelerator pedal is depressed sufficiently. In such an event, it is not possible to secure a good acceleration of the vehicle by using the maximum engine power. Therefore, it is desirable to devise a suitable measure for preventing such a problem.
Furthermore, if the vehicle is equipped with a system for controlling the engine rotational speed in accordance with the operating position of the accelerator pedal such as the CVT (continuously variable transmission), the engine rotational speed does not rise rapidly due to a delay of response of the system against the control even if the throttle valve is depressed rapidly for accelerating the vehicle. In other words, the throttle valve opening can not be increased rapidly, thus causing it impossible to secure the good acceleration of the vehicle. Therefore, it is desirable to devise a suitable measure for preventing such a problem.